1. Field
Implementations of the present invention relate generally to the passive detection of relative motion between a spectral imager and an electromagnetic-energy emitting source (i.e., an object or event) within a predetermined atmosphere exhibiting an atmospheric electromagnetic-absorption profile and, more particularly, to missile-threat warning systems. Each of various implementations further involves a method and associated apparatus for capturing and analyzing the spectral signature of the energy-emitting source and, based on an algorithmic analysis of the spectral signature at different times, rendering a determination as to whether distance between the spectral sensor and the object or event of interest has (i) increased, (ii) decreased or (iii) remained constant over a specified time interval.
2. Brief Description of an Illustrative Environment and Related Art
Passive threat warning systems detect potential missile threats to aircraft and other assets by sensing emitted energy in the ultraviolet, visible, and/or infrared bands emitted from the suspected threat. These systems rely on spectral sensors and algorithms to discern actual threats from background clutter, for example. At present, infrared sensor technology as applied to a missile threat warning application implements a system wherein the energy emitted in one narrow band, or color, in the range of approximately 4.4 μm to 4.8 μm is compared to the energy emitted in another narrow band in the range of approximately 3.9 μm to 4.1 μm. Discernment between, for example, a so-called “sun glint” and an earth-bound “hot object” or “hot event” such as a fire, a missile burn or a flamethrower is based upon the knowledge that the detectable energy associated with direct or reflected sunlight is markedly more intense in the 3.9 μm to 4.1 μm range than in the 4.4 μm to 4.8 μm range, while the emission spectrum of an earthbound hot event is generally more intense in the 4.4 μm to 4.8 μm range than in the 3.9 μm to 4.1 μm range. Although such a “two-color sensor” facilitates the elimination from consideration as threats certain types of clutter sources (e.g., sun glints), current systems are generally incapable of further discerning whether an event not eliminated as clutter under the initial two-color regime presents an actual threat (e.g., whether the source of the emitted energy is closing in or moving away from the sensor).
Accordingly, there exists a need for a method and associated apparatus adapted for the passive detection of relative motion between a spectral imager and an electromagnetic-energy emitting source (i.e., an object or event) within a predetermined atmosphere.